The present invention is directed toward analyzers for measuring vapor pressure and more particularly toward an air saturator for an analyzer that measures the Reid vapor pressure of volatile liquids.
The vapor pressure of a liquid or solid is the pressure exerted when the liquid or solid is in equilibrium with its own vapor. As such, vapor pressure is a measure of the tendency of a substance to vaporize and, thus, provides an indication of the volatility of the substance. The volatility of liquid fuel, such as gasoline, is important for both environmental and performance reasons. Fuel vapor is a major contributor to air pollution, which has prompted the Environmental Protection Agency (EPA) to enact regulations to limit evaporative fuel losses. In addition, if a fuel is too volatile and vaporizes too quickly, fuel flow within a vehicle may be adversely impacted so as to cause rough engine operation or stoppage. On the other hand, if fuel for a vehicle is not sufficiently volatile, the fuel may cause hard starting and poor warm-up of the vehicle, as well as unequal fuel distribution among the engine cylinders of the vehicle. For the foregoing reasons, it is important for fuel refiners to produce fuel with a volatility that provides optimal vehicle performance and meets environmental regulations. In order to do so, fuel refiners must be able to accurately measure the vapor pressure, more specifically, the Reid vapor pressure of the fuel they are producing. The Reid vapor pressure is the equilibrium pressure at 37.8° C. (100° F.) of a liquid having an initial boiling point above 0° C. (32° F.).
Since the Reid vapor pressure of a liquid mixture with differing component vapor pressures depends on a number of factors, such as the temperature, the ratio of vapor space to liquid volume in the liquid's container and the amount of dissolved air in the liquid mixture, standard test methods for measuring Reid vapor pressure have been established to reduce measurement variations due to these factors. One such standard test method has been established by the American Society for Testing Materials and is designated as ASTM D-323. In order to reduce variations in Reid vapor pressure measurement due to variations in air saturation, ASTM D-323 requires uniform saturation of a test sample with dissolved air at a temperature between 32° F. and 40° F. Since ASTM D-323 is adapted for use in a laboratory, ASTM D-323 specifies that the air saturation of a test sample is performed by manually shaking a container containing the test sample.
For most fuel refiners it is impractical to continuously perform manual tests on fuel samples in a laboratory. Therefore, fuel refiners typically measure Reid vapor pressure on a continual basis using Reid vapor pressure (RVP) analyzers. Conventional RVP analyzers do not saturate a test sample with air in accordance with ASTM D-3232. Instead, conventional RVP analyzers make corrections to compensate for the partial pressure of dissolved air which may be present in the samples tested. These corrections are not always accurate and may lead to inaccurate results.
Based on the foregoing, there is a need for an RVP analyzer having an air saturator that saturates test samples with air at a temperature between 32° F. and 40° F. The present invention is directed to such an RVP analyzer with an air saturator.